washingtonpost.com – Follow @pkcapitol Follow @eilperin Senate Democrats blocked a move Tuesday to compel construction of the Keystone XL pipeline, dealing a sharp loss to one of their own, Sen. Mary Landrieu (La.), who had pinned her chances for reelection on approval of the measure. The vote was a victory for environmental activists who have turned defeat of the pipeline into one of the central symbolic causes of their movement.